In the usual structure of an injection laser, current is sent across a p-n junction of two dissimilar type semiconducting layers to produce a nonequilibrium concentration of holes and electrons in a common recombination region. When these generated holes and electrons recombine, light is emitted in the region of the p-n junction. When operated as a laser with a Fabry-Perot cavity, the light is emitted along the length of the junction in a plane that is perpendicular to the direction of current flow through the junction.
It is desirable to alter or modify the geometry of light production across the above noted junction so that the light produced by the recombination of holes and electrons will be emitted in a direction that is perpendicular to the p-n junction plane. Such light direction output will enable one to construct a two dimensional array of injection lasers. Previous efforts to make an array of planar p-n junction laser light sources required auxiliary equipment independent of the light source or a complex grating feedback and coupling scheme. A representative array is the invention to M. F. Lamorte, U.S. Pat. No. 3,290,539 which issued on Dec. 6, 1966 on an application filed Sept. 16, 1963. However, in the Lamorte structure, a sheet of a light reflecting material, such as aluminum, is punched with a plurality of holes, each hole being shaped to serve as a parabolic reflector. This sheet, containing the plurality of light reflectors, is positioned over an array of p-n junction lasers so as to reflect the light from each junction in a direction perpendicular to the plane of that junction. However, such punched out sheet of aluminum is separate from each p-n junction laser and one is faced with the problem of positioning each fixed reflector over each fixed p-n junction, yet attain uniform light emission from each laser.
Complex injection laser structures using diffraction gratings for feedback and coupling the light out in a direction parallel to the current flow have been described by Comerford and Zory and others; for example, see an article entitled "Selectively Etched Diffraction Gratings in GaAs" published in Applied Physics Letters, Volume 25, page 208, 1974 and bibliography therein.
The present invention achieves an array of p-n junction lasers by chemically etching opposing sides or walls of a plurality of p-n junctions, deposited, by conventional lithographic techniques, whereby the etchant chosen preferentially cuts away such walls at an angle of approximately 45.degree. to the plane of a p-n junction. Such 45.degree. angled walls serve as mirrors that reflect the lasing light of the p-n junction in the direction of electrical current flow through the junction. Not only are these 45.degree. mirrors part of the optical cavity of the p-n junction laser, but they are integral with the laser, per se, and, as such, serve to achieve an array of lasers wherein the alignment problems are minimized.
Thus, it is an object of this invention to attain a folded cavity effect for each injection laser of an array of lasers so as to permit lasing light to emanate from a p-n junction laser perpendicularly to the plane of that p-n junction.
It is yet another object to change the geometry of an injection laser so that the means for modifying the direction of light output from that junction laser is integral with that laser.
A further object is to provide a novel two dimensional laser array wherein the method of manufacturing the array achieves uniformity of performance of each laser in that array.